Methods. Patients enrolled in the German biologics register between May 2001 and September 2003 were included. Treating rheumatologists assessed adverse events and serious adverse events. All adverse events and serious adverse events experienced within 12 months after study entry were analyzed. Propensity score methods were applied to estimate which part of a rate increase was likely to be attributable to differences in patient characteristics.

Results. Data were available for 512 patients receiving etanercept, 346 patients receiving infliximab, 70 patients receiving anakinra, and 601 control patients treated with disease-modifying antirheumatic drugs. The total number of adverse events per 100 patient-years was 22.6 (95% confidence interval [95% CI] 18.7-27.2) among patients receiving etanercept, 28.3 (95% CI 23.1-34.7) among patients receiving infliximab, and 6.8 (95% CI 5.0-9.4) among controls (P < 0.0001). Significant differences in the rate of serious adverse events were also observed. For patients receiving etanercept, those receiving infliximab, and controls, the total numbers of serious adverse events per 100 patient-years were 6.4 (95% CI 4.5-9.1), 6.2 (95% CI 4.0-9.5), and 2.3 (95% CI 1.3-3.9), respectively (P = 0.0016). After adjusting for differences in the case patient mix, the relative risks of serious adverse events were 2.2 (95% CI 0.9-5.4) for patients receiving etanercept and 2.1 (95% CI 0.8-5.5) for patients receiving infliximab, compared with controls.

Conclusion. Patients treated with biologic agents have a higher a priori risk of infection. However, our data suggest that this risk is increased by treatment with tumor necrosis factor inhibitors.